feat: Add PdfAttachmentController with CheckAttachments endpoints

- Add POST /api/pdf/attachments/check endpoint (multipart/form-data)
- Add POST /api/pdf/attachments/check endpoint (application/json with Base64)
- Dual input support: IFormFile (file upload) and Base64 JSON
- Controller converts IFormFile → byte[] and sends to MediatR
- Complete XML documentation with Swagger examples
- Primary constructor pattern used

DocumentOperator.API/Controllers/PdfAttachmentController.cs

@@ -0,0 +1,85 @@
+using DocumentOperator.Application.CheckPdfAttachments.Queries;
+using DocumentOperator.Application.Common.DTOs;
+using MediatR;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Mvc;
+
+namespace DocumentOperator.API.Controllers;
+
+/// <summary>
+/// Controller for PDF attachment operations (detection, extraction, embedding)
+/// </summary>
+[ApiController]
+[Route("api/pdf/attachments")]
+[Produces("application/json")]
+public class PdfAttachmentController(IMediator mediator) : ControllerBase
+{
+    /// <summary>
+    /// Checks if a PDF contains embedded files (attachments) and returns their metadata.
+    /// Supports multipart/form-data file upload.
+    /// </summary>
+    /// <param name="file">The PDF file to check for attachments</param>
+    /// <param name="cancellationToken">Cancellation token</param>
+    /// <returns>Attachment check result with metadata for all found attachments</returns>
+    /// <response code="200">PDF successfully checked - returns attachment details</response>
+    /// <response code="400">Invalid input (file missing, not a PDF, or corrupted)</response>
+    /// <response code="500">Internal server error during PDF processing</response>
+    [HttpPost("check")]
+    [Consumes("multipart/form-data")]
+    [ProducesResponseType(typeof(AttachmentCheckResult), StatusCodes.Status200OK)]
+    [ProducesResponseType(typeof(ProblemDetails), StatusCodes.Status400BadRequest)]
+    [ProducesResponseType(typeof(ProblemDetails), StatusCodes.Status500InternalServerError)]
+    public async Task<IActionResult> CheckAttachmentsFromFile(
+        IFormFile file,
+        CancellationToken cancellationToken)
+    {
+        // Convert IFormFile to byte array
+        using var memoryStream = new MemoryStream();
+        await file.CopyToAsync(memoryStream, cancellationToken);
+        byte[] pdfBytes = memoryStream.ToArray();
+
+        // Send query to MediatR (ValidationBehavior runs automatically)
+        var query = new CheckPdfAttachmentsQuery { PdfBytes = pdfBytes };
+        var result = await mediator.Send(query, cancellationToken);
+
+        return Ok(result);
+    }
+
+    /// <summary>
+    /// Checks if a PDF contains embedded files (attachments) and returns their metadata.
+    /// Supports Base64-encoded PDF via JSON payload.
+    /// </summary>
+    /// <param name="request">Request containing Base64-encoded PDF</param>
+    /// <param name="cancellationToken">Cancellation token</param>
+    /// <returns>Attachment check result with metadata for all found attachments</returns>
+    /// <response code="200">PDF successfully checked - returns attachment details</response>
+    /// <response code="400">Invalid input (Base64 format error, not a PDF, or corrupted)</response>
+    /// <response code="500">Internal server error during PDF processing</response>
+    [HttpPost("check")]
+    [Consumes("application/json")]
+    [ProducesResponseType(typeof(AttachmentCheckResult), StatusCodes.Status200OK)]
+    [ProducesResponseType(typeof(ProblemDetails), StatusCodes.Status400BadRequest)]
+    [ProducesResponseType(typeof(ProblemDetails), StatusCodes.Status500InternalServerError)]
+    public async Task<IActionResult> CheckAttachmentsFromBase64(
+        [FromBody] CheckPdfAttachmentsRequest request,
+        CancellationToken cancellationToken)
+    {
+        // Send query to MediatR (ValidationBehavior runs automatically)
+        var query = new CheckPdfAttachmentsQuery { Base64Pdf = request.Base64Pdf };
+        var result = await mediator.Send(query, cancellationToken);
+
+        return Ok(result);
+    }
+}
+
+/// <summary>
+/// Request DTO for Base64-encoded PDF attachment check
+/// </summary>
+public record CheckPdfAttachmentsRequest
+{
+    /// <summary>
+    /// PDF document encoded as Base64 string
+    /// </summary>
+    /// <example>JVBERi0xLjQKJeLjz9MKMSAwIG9iago8PC9UeXBlL0NhdGFsb2c...</example>
+    public string Base64Pdf { get; init; } = string.Empty;
+}